Althea is an IMAP email client for X that uses the GTK widget set. It was built with the IMAP protocol in mind in order to avoid many of the pitfalls experienced by POP clients that added IMAP support. Althea allows easy access to a nearly unlimited number of servers, and has a very small memory footprint. As of version 0.5.0 Althea also supports IMAP over SSL.

Arrow is an elegant, powerful, graphical interface to electronic mail. This is not just another single window mail reader. Instead, it displays each mailbox and message in a separate window, thereby allowing one to simultaneously open as many mailboxes and view and compose as many messages as one wishes. This paradigm also allows one to drag-and-drop text between messages and organize ones mail by dragging messages between mailboxes.

AUC (Authenticated User Community) is an intranet system designed for use in an educational organization but is also useful in many other settings. It offers the ability for users to have a uniform web-based interface to discussion forums, e-mail (similar to hotmail, etc.), file management, and a searchable user database. Also, "Interactive Classrooms" provide a means for students and teachers to have a web-based extension to their in-class interaction. The system runs from a C-based monolithic CGI script. MySQL is used for database storage. Also, the web-based mail client supports MIME parts/attachments, IMAP, mbox, and multiple mail folders.

Balsa is a Gnome e-mail client supporting POP3,
IMAP, and local mail delivery. It can be compiled
with multi-threading support for faster response,
and can do nifty things like read your GnomeCard
address book, use LDAP, and render HTML mail.

BasiliX is a webmail application based on PHP and IMAP, and powered with the MySQL database server. It supports simple mail actions, sending/receiving attachments, an addressbook with group capability, settings utility, multiple languages, multiple folders and themes.

Beonex Communicator is Mozilla polished for end users. It contains Navigator, Mailnews, Composer, and ChatZilla. Navigator has support for key web standards and a convenient interface. For example, it eases searching the Internet, similar to Apple's Sherlock on Macintosh. The Bookmark Manager can deal with huge collections of bookmarks and allows you to overview and sort them while you are surfing. If you want, you can track the latest headlines or webcams using the Sidebar. The Mailnews client supports multiple IMAP, POP3 and/or news accounts for each user, so you can download and manage all your email from various accounts in one place and store them on your computer or the server. Beonex puts a strong emphasis on security, privacy, and netiquette, to protect the private or confidential information on your computer and to encourage fairness.

This is a PHP class that attempts to validate a given e-mail address at four levels: matching the address against a RFC compliant regular expression; checking whitelists and blacklists of domains with typing mistakes, disposable email addresses, and temporary and fake domains; verifying the existence of the destination SMTP server by verifying the respective DNS MX record; and connecting to that server to see if the given address is accepted as a valid recipient. The class also features a debugging output option that lets you see the remote SMTP server connection and data exchange dialog to see the real cause why an apparently valid address may not be accepting messages.

MailMan is one of the most stable, mature, and robust Web-based email systems available. The overall goal of the system is to provide the simplest possible way to add a Web-based email system to any Web site, so ease of installation and maintenance was the first goal in MailMan's design. It has no dependencies and no known incompatibilities with any Web server or mail server. It supports sending and receiving attachments, a single-frame or multi-frame interface, HTML-formatted messages, user options, address books, mail folders, and more.